In the field of engines, e.g., combustion engines as used in the automotive field, rotation of a cam shaft may be sensed and be used for controlling injection of fuel into combustion chambers of the engine. For example, the current rotational angle of the cam shaft may be used for setting a timing of injection of air-fuel mixture, duration of the injection, or opening and dwell angles of valves used for the injection of fuel.
A known way of sensing rotation of the cam shaft is to place a ferromagnetic toothed wheel on the cam shaft and use a Hall sensor to detect passing of teeth of the toothed wheel. The output of such Hall sensor corresponds to a pattern of pulses in which the frequency of pulses varies according to the speed of rotation. By giving the different teeth of the toothed wheel a size which is distinctive with respect to other teeth of the toothed wheel, it becomes also possible to distinguish between different angular positions in the course of a single rotation of the cam shaft.
However, evaluation of the current rotation angle using such toothed wheel requires that the cam shaft is actually rotating. Further, complex algorithms may be needed for accurately estimating the current rotation angle from the sensed pattern of pulses. Also, the achievable accuracy may significantly depend on manufacturing accuracy of the toothed wheel.
Accordingly there is a need for techniques which allow for sensing rotation of a cam shaft of an engine in an efficient and accurate manner.